The present invention concerns aircraft landing gear. More particularly, but not exclusively, this invention concerns multi-wheel landing gears comprising at least one steerable axle. The invention also concerns a locking mechanism for a multi-wheel landing gear bogie including a steerable axle.
Multi-wheel landing gears are often used on large aircraft, for example the Airbus A380. The multi-wheel landing gears are used to support the large loads exerted on the landing gears by the aircraft when taxiing, at take-off, and landing. In order to prevent excess tyre wear caused by tyre scrubbing during taxiing, the multi-wheel landing gear may include at least one pair of wheels mounted on a steerable axle. At other times, for example during take-off and landing, it is necessary to lock the steerable axle in the straight ahead position.
Typically, in a multi-wheel landing gear, the steerable axle is pivotally mounted to the landing gear bogie. The steerable axle is steerable by an actuator which may extend and retract in order to change the orientation of the steerable axle. In a known arrangement, the landing gear includes a locking mechanism that comprises a wedge-shaped lock member that is pivotally mounted to the landing gear bogie. The wedge-shaped lock member is arranged to be received between two bearing pads mounted on the steerable axle in order to lock the steerable axle in a ‘straight ahead’ position for taxi, take off, and landing. The wedge-shaped lock member is secured in the locked position by two springs that act to pull the wedge-shaped lock member into engagement with the bearing pads. An actuator is arranged to act against the springs in order to move the wedge-shaped lock member from away from the bearing pads, such that the steerable axle is unlocked and pivotal movement, away from the straight ahead position, is allowed.
FIG. 1 shows a schematic cross-sectional view of this known locking mechanism 1. FIG. 1 shows a portion of the steerable axle 2 having a recess 4 containing two bearing pads 6. The two bearing pads 6 are located on opposite sides of the recess 4 and face each other. Each bearing pad is fixed to the axle 2 using a fixing 8. In the locked position as shown in FIG. 1, a lock member 10 is located in the space between the bearing pads 6. The far end 6a of each bearing pad 6 is hooked to prevent movement of the lock member 10 deeper into the space between the bearing pads 6. Each bearing pad 6 is in contact with a corresponding side of the lock member 10. The front corners 10a of the lock member 10 are bevelled giving the lock member 10 a wedge shape.
Time and/or skill may be required to bring the lock member into sufficient alignment with the bearing pads so that it can move into engagement with the bearing pads. If the lock member 10 is not very closely lined up with the bearing pads 6 when attempting to lock the steerable axle 2, the lock member 10 may not be able to move into the space between the bearing pads 6. In that case, the steerable axle 2 would not be fully locked, and the aircraft would not be able to take off until the problem is fixed; this may cause delays to the aircraft departure time or the grounding of the aircraft.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved landing gear mechanism.